1. Field of the Invention
The present invention relates to a thrust roller bearing and more particularly, to a thrust roller bearing that can be used under a thin lubrication or high-speed rotation environment.
2. Description of the Background Art
A thrust roller bearing used in a compressor for a car air conditioner, an automatic transmission, a manual transmission or a hybrid car is required to have characteristics that can be used under a severe usage environment such as a high-speed rotation or thin lubrication environment upon request of energy saving, miniaturization and high-power output of recent years. The thrust roller bearing that can be used under the severe usage environment is disclosed in Japanese Unexamined Patent Publication No. 2003-83333, Japanese Unexamined Patent Publication No. 2005-164023, or Japanese Unexamined Patent Publication No. 2004-301195.
Hereinafter, the manufacturing method of a retainer contained in the thrust roller bearing disclosed in the Japanese Unexamined Patent Publication No. 2004-301195 will be briefly described. First, pockets for holding rollers are punched out by a punch and the like. Then, an inner flange part of the retainer is formed by bending a part on the inner side of the retainer in the rotation axis direction. Then, an outer flange part that extends to the outer end of the pocket is formed by bending a part on the outer side of the retainer to be positioned, inside the outer end part of the pocket. Thus, the retainer is manufactured.
According to the Japanese Unexamined Patent Publication No. 2003-83333 and the Japanese Unexamined Patent Publication No. 2005-164023, the thrust roller bearing comprises rollers having the curved end surfaces and a retainer. Thus, sliding resistance between an outer end surface of the roller and an outer wall surface of the pocket can be small, so that wear of the outer wall surface of the pocket can be restricted.
In addition, according to the Japanese Unexamined Patent Publication No. 2004-301195, the outer wall surface of the pocket is comprised of the flange part bent in the rotation axis direction. Thus, the area of the outer wall surface of the pocket can be large and the contact surface pressure applied from the outer end face of the roller can be small, whereby the wear of the outer wall surface of the pocket can be restricted.
However, according to the retainers disclosed in the in Japanese Unexamined Patent Publication No. 2003-83333, the Japanese Unexamined Patent Publication No. 2005-164023, and the Japanese Unexamined Patent Publication No. 2004-301195, the outer wall surface of the pocket is the surface of an iron plate. The surface of the iron plate is a coarse surface and the degree of its surface roughness is low. In addition, even when the outer wall surface of the pocket is formed of the surface punched out by the punch, the degree of its surface roughness is also low. When the outer end face of the roller abuts on the outer wall surface of the pocket having low degree of surface roughness, drilling wear is generated. Here, the drilling wear means a phenomenon in which when the end face of the roller, the outer end face thereof, especially is pressed to the outer wall surface of the pocket due to centrifugal force and the like and further pressed thereto due to the rotation of the roller, abnormal wear is generated on the outer wall surface of the pocket. Especially under the above severe usage environment, this is conspicuous. Thus, the outer wall surface of the pocket is considerably worn out and thrust roller bearing is not expected to have a long life.
Furthermore, since force such as centrifugal force is applied to the outer wall surface of the pocket while the roller is rolling, when the outer wall surface of the pocket does not have enough strength, it could be damaged. In this case also, the thrust roller bearing is not expected to have a long life.
In addition, when the roller has a small diameter, it is difficult that the end face of the roller is appropriately in contact with the outer wall surface of the pocket through the above manufacturing method.